1. Field of the Invention
The present invention relates to an electric double-layer capacitor, and more particularly, it relates to an electric double-layer capacitor which has an improved structure for sealing an opening end portion of its case. It also relates to a copending, commonly assigned application, Ser. No. No. 048,220 filed May 11, 1987 and now U.S. Pat. No. 4,766,523 issued Aug. 23, 1988.
2. Description of the Prior Art
In a conventional electric double-layer capacitor which is hereinafter referred to as prior art example 1, a plurality of elements are generally stacked and integrated by a thermal contraction tube (heat-shrinkable tube) and an electrode structural member formed of electrode plates and an insulating plate is placed on the same. Such components are inserted in a case, an opening end portion of which is then caulked (crimped) and the outer peripheral portion thereof is covered by another thermal contraction-tube.
In another type of a conventional electric double-layer capacitor which is hereinafter referred to as prior art example 2, a crimped portion at an opening end of a can case is sealed by ultraviolet-setting resin or thermosetting resin in order to ensure air-tightness of the crimped portion of the case.
In the prior art example 1, however, the element structure may become swollen or softened or metal parts may be rusted by infiltration of an organic solvent or water, since the opening end portion of the can case is not sufficiently sealed. Further, because of the insufficient seal the electrolytic solution maybe volatilized to cause performance degradation, such as an increase in equivalent series resistance or a decrease in electrostatic capacity.
In the prior art example 2, inferiority in airtightness may be caused by a variation in the volume of the injected resin or inferior wetting of the same. Further, the injected resin may spread upwardly toward the free ends of the electrode terminals, to cause a problem in employment of the electric double-layer capacitor.